Loading calculation

ABSTRACT

A system and method for determining loads throughout a power distribution network having a plurality of switching devices provided along a feeder. The method includes measuring the current and/or voltage on one or both sides of the switching devices and calculating a power flowing through each of the switching devices and a load in each section using the current and/or voltage measurements at predetermined sample times. The method further includes storing a plurality of recorded current/voltage measurements or calculated powers flowing through each device for consecutive sample times. The method then determines a median load from the measurements and power flows and calculates a load in each of network sections.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from the U.S.Provisional Application No. 63/153,657, filed on Feb. 25, 2021, thedisclosure of which is hereby expressly incorporated herein by referencefor all purposes.

BACKGROUND Field

The present disclosure relates generally to a system and method fordetermining loads throughout a power distribution network and, moreparticularly, to a system and method for determining loads throughout apower distribution network having a plurality of switching devicesprovided along a feeder.

Discussion of the Related Art

An electrical power network, often referred to as an electrical grid,typically includes power generation plants each having power generators,such as gas turbines, nuclear reactors, coal-fired generators,hydro-electric dams, etc. The power plants provide power at mediumvoltages that are then stepped up by transformers to a high voltage ACsignal to be connected to high voltage transmission lines that deliverelectrical power to substations typically located within a community,where the voltage is stepped down to a medium voltage for distribution.The substations provide the medium voltage power to three-phase feedersincluding three single-phase feeder lines that carry current 120° apartin phase. three-phase and single-phase lateral lines are tapped off ofthe feeder that provide the medium voltage to various distributiontransformers, where the voltage is stepped down to a low voltage and isprovided to loads, such as homes, businesses, etc.

Periodically, faults occur in the distribution network as a result ofvarious things, such as animals touching the lines, lightning strikes,tree branches falling on the lines, vehicle collisions with utilitypoles, etc. Faults may create a short-circuit that increases the load onthe network, which may cause the current flow from the substation tosignificantly increase, for example, many times above the normalcurrent, along the fault path. This amount of current causes theelectrical lines to significantly heat up and possibly melt, and alsocould cause mechanical damage to various components in the substationand in the network. Many times the fault will be a temporary orintermittent fault as opposed to a permanent or bolted fault, where thething that caused the fault is removed a short time after the faultoccurs, for example, a lightning strike, and where the distributionnetwork will almost immediately begin operating normally.

Fault interrupters, for example, reclosers that employ vacuuminterrupters, are provided on utility poles and in underground circuitsalong a power line and have a switch to allow or prevent power flowdownstream of the recloser. These reclosers detect the current andvoltage on the line to monitor current flow and look for problems withthe network circuit, such as detecting a fault. If fault current isdetected the recloser is opened in response thereto, and then after ashort delay closed to determine whether the fault is a temporary fault.If fault current flows when the recloser is closed, it is immediatelyopened. If the fault current is detected again or two more times duringsubsequent opening and closing operations indicating a permanent fault,then the recloser remains open, where the time between detection testsmay increase after each test. For a typical reclosing operation forfault detection tests, about 3-6 cycles of fault current pass throughthe recloser before it is opened.

When a fault is detected, it is desirable that the first faultinterrupter upstream from the fault be opened as soon as possible sothat the fault is quickly removed from the network so that the loadsupstream of that fault interrupter are not disconnected from the powersource and service is not interrupted to them. It is further desirablethat if the first fault interrupter upstream from the fault does notopen for whatever reason, then a next fault interrupter upstream fromthe fault is opened, and so on. In order to accomplish this, it isnecessary that some type of communications or coordination protectionscheme be employed in the network so that the desired fault interrupteris opened in response to the fault.

A sectionalizer is a self-contained, circuit-opening device used incombination with source-side protective devices, such as reclosers orcircuit breakers, to automatically isolate faulted sections of anelectrical distribution network. A faulted circuit indicator is a devicethat automatically detects and identifies faults in an electricaldistribution network, but does not have switching capabilities to open apower line. The devices are typically distributed between and among thereclosers to provide a system for isolating smaller sections of thenetwork in response to a fault. Faulted circuit indicators andsectionalizers rely on observing a sequence of fault currents and thepresence and absence of voltage either to indicate the presence of afault or count the number of reclosing attempts, and then performcircuit isolation sectionalizing when the desired number of reclosingattempts has been reached. Existing power distribution circuitsectionalizers detect the passage of fault currents, including both theinitial fault event and subsequent recloser-initiated events, as part ofmore elaborate fault isolation and restoration processes. Theseprocesses may include counting discrete intervals of fault currentpassage, or counting discrete intervals of voltage presence and absence.

Modern power distribution networks of the type being discussed hereinusually operate as intelligent distribution automation systems, i.e.,provide intelligent control over electrical power grid functions to thedistribution level and beyond, where the many of the devices talk toeach other and perform functions based on received information and data.These systems require device control that needs to have knowledge of thesystem topology, i.e., the architecture, for automation tasks, where themain purpose of the knowledge dissemination is to enable automatic powerrestoration in response to faults. For example, to decide what extranetwork sections alternative power sources can power, the automaticpower restoration will need the relevant network information, such aspower being consumed in each section.

In existing distribution automation systems, the system topology needsto be manually pushed to the devices for distributed control or acontrol center for centralized control, both at deployment and everytime the topology of the network changes. In other words, the topologyof the system needs to be manually loaded into each device, and thus thetopology stored in each device is not automatically changed when thetopology changes from devices being added to or removed from the networkor when switching events occur to isolate faults. This not only requiresa significant amount of engineering work, but also complicates the logicwhen the system topology changes due to automated operations. Further,if a switching device automatically opens, such as in response to afault, other devices may not be made aware of this switching.

SUMMARY

The following discussion discloses and describes a system and method fordetermining loads throughout a power distribution network, where thenetwork includes at least one power source, a primary feeder, aplurality of switching devices positioned along the primary feeder thatare in communication with each other or with a centralized control in acontrol center, and sections each of which consists of power linesbounded by switching devices or other current measuring devices. Themethod includes measuring current and voltage or just current on one orboth of an X side and a Y side of each of the switching devices, andcalculating power flowing through each of the switching devices usingcurrent and voltage or just current measurements at predetermined sampletimes. The method further includes storing a plurality of the calculatedpowers for consecutive sample times. The method then determines a medianpower from a predetermined number of the stored powers, sends the medianpower from the switching devices to a control device or multiple controldevices, and calculates a power in each of the sections in the controldevice.

Additional features of the present disclosure will become apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic type diagram of an electrical powerdistribution network;

FIG. 2 is a simplified schematic block diagram of a switching device inthe network shown in FIG. 1;

FIG. 3 is a simplified schematic type diagram of an electrical powerdistribution network illustrating an extreme linear case for a datadissemination process;

FIG. 4 is a simplified schematic type diagram of an electrical powerdistribution network illustrating another extreme case for a datadissemination process; and

FIG. 5 is a simplified schematic type diagram of an electrical powerdistribution network for describing load calculations.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the disclosure directedto a system and method for determining loads throughout a powerdistribution network having a plurality of switching devices providedalong a feeder, where the method includes calculating the loads infeeder sections, saves consecutive calculated loads, and provides amedian of the saved loads is merely exemplary in nature, and is in noway intended to limit the disclosure or its applications or uses.

This disclosure proposes providing a dynamic graph representation forrobust data dissemination between switching devices in a powerdistribution network that can operate with partial data resulting fromcommunications problems. The dynamic graph representation allows theswitching devices that isolate faults in the network to automaticallyobtain the network topology with minimal manual input at devicedeployment, and enables an automatic topology update in all of thedevices when the topology changes. The switching devices in the networkare capable of measuring voltage and/or current, and sending that datato other devices or a control center by, for example, wirelesstransmissions, cellular, fiber optics, etc. In the discussion below, ateam is defined as a section of powerlines bounded by switching devices.In the discussion below, the device performing the loading computationis sometimes referred to as the control, where the control may reside inone or multiple switching devices, a substation or control center. Therewill be data specific for each switching device, such as open/closedstatus, and data specific for each team, such as amount of load andwhether there is a fault within the team. A device list stores devicedata and a team list stores team data of all of the devices and teams ina certain region of the network. The boundary of this region isspecified by the distribution automation scheme.

FIG. 1 is a simplified schematic type diagram of an electrical powerdistribution network 10 that employs distributed control. The network 10includes two AC sources 12 and 14, such as electrical substations thatstep down high voltage power from a high voltage power line (not shown)to medium voltage power. The network 10 also includes switching devices28, 30, 32 and 34 that can be any suitable device for the purposesdiscussed herein, such as reclosers, breakers, sectionalizers, etc. Thedevices 28, 30 and 34 are normally closed devices and the device 32 is anormally open device. This configuration defines a feeder 18 between thesource 12 and the devices 32 and 34 and a feeder 20 between the source14 and the device 32. Lateral lines 22 are coupled to the feeder 18 andfeed loads 24. A line section 38 of the feeder 18 is provided betweenthe source 12 and the device 28, a line section 40 of the feeder 18 isprovided between the devices 28 and 30, a line section 42 of the feeder18 is provided between the devices 30, 32 and 34, a line section 44 isconnected to the source 14, and a line section 46 is connected to thedevice 34. The source 12 provides power to the sections 38, 40 and 42and the source 14 is prevented from proving power to the sections 38, 40and 42. A distributed generation (DG) source 36, such as solar, wind,turbine, battery, etc., is provided in the section 40.

The combination of the AC source 12, one side of the device 28 and thesection 38 define a team, the combination of one side of the devices 28and 30 and the section 40 define a team, the combination of one side ofthe devices 30, 32 and 34 and the section 42 define a team, thecombination of one side of the device 32, the source 14 and the section44 define a team, and the combination of one side of the device 34 andthe section 46 define a team, where some of the teams define a division48 and where the devices 32 and 34 are also tie devices betweendivisions. As will be discussed in detail below, the topology, i.e.,device configuration, of the division 48 will be known by all of thedevices 28-34 by communications therebetween, where the topology of thedivision 48 will be automatically revised and updated as devices areremoved and added to the network 10. A control center 50 may be in, forexample, radio communication with the switching devices 28-34 thatprovides switching control consistent with the discussion herein.

FIG. 2 is a simplified schematic block diagram of a switching device 60intended to be a non-limiting general representation of any one of theswitching devices 28-34 in the network 10, where the device 60 mayinclude a switch 62, voltage/current sensors 64, a control device 66(sometimes referred to herein as the control), a memory 68, having asize of N+1, and a transceiver 70, where the device list and the teamlist may be stored in the memory 68. Further, for some device designsdiscussed below, the memory 68 is intended to represent a separatememory on each of the upstream and downstream sides of the device 60.The switching device 60 may also include a timer 72 and a median filter74 for reasons that will become apparent from the discussion below.

The topology of the power distribution network 10 is represented byspecific fields in the device list and the team list, where Tables 1 and2 below are an example of the device list and the team list,respectively, stored in each of the switching devices 28-34corresponding to the division 48. The local indices ordering of thedevices in the device list and the teams in the team list are differentin different devices. The device local index identifies each device inthe division 48 separately from the device ID and the team local indexidentifies the teams in the division 48. The local indices are onlymeaningful and can identify a device or team in a specific devicesmemory 68. It is noted that the teams do not need global indexing orIDs, where each team is uniquely identified by the devices on the team.This makes a split or a union of the teams due to the addition orremoval of a device easy to accomplish. The device specific data and theteam specific data in the lists can be anything relating to that deviceor team, such a voltage measurements, current measurements, open/closedstatus, etc. Besides the device specific data, each device in the devicelist includes two fields, namely, a TeamOnX field that specifies thelocal index in the team list of the team on each device's X side, and aTeamOnY field that specifies the local index in the team list of theteam on each device's Y side, where the X and Y sides of a device aredetermined by the physical orientation of the device when it isinstalled. Knowing the orientation of the devices is necessary becausethese devices are often capable of measuring voltage on both sides ofthe device. Each team in the team list includes a DevicesOnTeam fieldthat specifies the local indices in the device list (not device ID) ofthe devices on that team.

TABLE 1 Local Index ID TeamOnX TeamOnY Device Specific Data 1 28 A B — 230 B C — 3 32 C D — 4 34 C E —

TABLE 2 Local Index DevicesOnTeam Team Specific Data A 1 — B 1, 2 — C 2,3, 4 — D 3 — E 4 —

The TeamOnX field and the TeamOnY field in the device list point to thelocal indices of the entries in the team list, and the DevicesOnTeamfield in the team list points to the local indices of the entries in thedevice list (not device IDs). This makes it faster to access theinformation of the devices on a team, and the information of teams oneach side of a switching device by eliminating the need for searches.Further, the device local indices in the DevicesOnTeam field are sortedby the device ID. For example, the DevicesOnTeam field for Team C is theswitching devices 30, 32 and 34. Because a team is uniquely identifiedby the devices on the team, this makes the comparison between two teamseasier. Specifically, if two teams have the same number of devices, andthe devices have the same device IDs pairwise, then they are the sameteam.

The topology of the division 48 can be recovered from either the devicelist or the team list, and thus the two lists provide mutual validation.In other words, if the topology recovered from the device list and thetopology recovered from the team list are inconsistent, then there is anindication of data errors. Moreover, the two lists also make thetraversal of the graph more efficient. For example, if a switchingdevice needs to know which teams are adjacent to Team A, it only needsto read which devices are on Team A in its team list, and which teamsare connected to these devices in its device list. By contrast, for thesame task, if only the team list contains network topology information,after reading the devices connected to Team A in the team list, thedevice will need to search through all of the teams to find which teamis connected to those devices.

This graph representation makes it possible to automatically discoverthe network topology by any of the switching devices. Knowing thetopology of the network 10 or the division 48 allows power restorationin response to a fault, so that when there is a fault and loads aredropped, knowledge of which loads have been dropped and how big theloads are allows how the open and closed status of the switching devices28-34 is determined so that alternate sources can be connected to someof the loads.

At deployment of a device, the engineer only needs to manually specifythe immediate neighbor devices on each side of the new device and thenthe topology of the whole division 48 can be provided in all of thedevices 28-34 by transferring information and data from device todevice. The newly deployed device will automatically build its owndevice list and team list with this initial information. After sharingthis information through automated communications, the control mayeasily populate the corresponding fields in its device list and teamlist and have the topology information of the full division 48. Forexample, in the network 10, if the control is in the switching device28, then it can start the device list and the team list with theinformation of its immediate neighbor devices, as shown by Tables 3 and4 below.

TABLE 3 Local Index ID TeamOnX TeamOnY . . . 1 28 A B 2 30 B

TABLE 4 Local Index DevicesOnTeam . . . A 1 B 1, 2

When the switching device 28 receives a message that containsinformation about the switching device 30 and the immediate neighbordevices of the device 30, it can update its device and team lists, asshown in Tables 5 and 6, respectively, below. It is noted that the localindices in the message can be different than the local indices in thecontrol. Tables 7 and 8 are the updated device and team lists,respectively, in the memory of the device 28 after processing themessage.

TABLE 5 Local Index ID TeamOnX TeamOnY . . . 1 30 A B 2 28 A 3 32 B 4 34B

TABLE 6 Local Index Local Team Indices . . . A 2, 1 B 1, 3, 4

TABLE 7 Local Index ID TeamOnX TeamOnY . . . 1 28 A B 2 30 B C 3 32 C 434 C

TABLE 8 Local Team Indices . . . A 1 B 1, 2 C 2, 3, 4

After receiving the information of the device 32 and the device 34 insubsequent messages, the complete device and team lists will be built inthe memory 68 of the device 28. One possible reason that the device 28may not have had the topology information beyond the device 30 is thatthe system was just initialized. Another possible reason is that thedevice 30 previously defined the boundary of a division, and because ofa change in its status, the two divisions on its two sides are nowcombined as one division.

For each switching device identified in a message, the recipient devicechecks if it already has that device in its device list. The same isdone for each team. To avoid searches for these checks, the recipientswitching device maintains a mapping between the local indices of thedevice list and the team list in the incoming messages from a specificmessage source, for example, a switching device, and the local indicesof those lists in its own memory. When the recipient device checkswhether it already has a device from the message in its own device list,it uses the map to see if this device maps to the same device in itsdevice list. If yes, then the device updates the information in itsdevice list using the message and, if no, then the device updates themapping before updating its device list. The same procedure applies tothe team list. Note that none of the incoming messages needs to convey afull view of the network. As long as the whole network is covered by allincoming messages, the recipient will have up-to-date information of thenetwork. If a message is lost, a device may only have outdatedinformation for the part of the network covered by that message. If thenetwork is designed such that each device calculates its localinformation, such as team loading, possibly by gathering data from itsimmediate neighbor devices, and propagates the result out to otherdevices, then the process requires no central processing.

When a new switching device is added to the network 10, this device onlyneeds to be manually added to its immediate neighbor device's settingsas their new neighbor device, and the device lists and team lists ofthese neighbor devices will update themselves accordingly. As requiredbefore, the new device will also only need its own immediate neighbordevices as the manual input in its setting. The data dissemination willthen propagate the addition of the device automatically to other devicesthat need the topology information. Similarly, when a device is removedfrom the network 10, only its immediate neighbor devices will need to beupdated manually, and the updated topology information will propagateautomatically to other devices that need the topology information.

The processes described above only adds or updates existing elements(devices and teams) to the lists, and does not remove elements from thelists. Elements do need to be removed from the lists if a device istaken out of the system, or a division is split into two divisionsbecause a device becomes a boundary device. To accomplish the removal ofdisconnected elements, a graph traversal, such as breadth first search(BFS) or a depth first search (DFS), well known to those skilled in theart, is initiated starting from the device in which the control resides.This graph traversal indicates all the elements that are still withinthe division 48. Therefore, every element that hasn't been reached bythe graph traversal is removed.

As discussed above, in a power distribution network that employsdistributed control, knowledge acquired from each of the switchingdevice 28-34 needs to be disseminated through the division 48 so thatevery device 28-34 in the division 48 has the knowledge, where thedivision 48 is the basic unit for distribution automation tasks, such asautomatic power restoration. For example, to decide what extra networksections each alternative source can power, the automatic powerrestoration will need the relevant network information, such as powerbeing consumed in each of the sections. Knowledge dissemination can alsobe used for other purposes, such as supporting voltage regulationdecisions.

This disclosure also proposes a knowledge or data dissemination methodthat enables the switching devices 28-34 to efficiently share theirknowledge across the network 10. At the end of each data disseminationperiod, each of the switching devices 28-34 will have up-to-dateknowledge about all of the other devices 28-34 in the division 48.Compared to existing methods, this knowledge dissemination methodminimizes the number of messages passed between the devices 28-34 aswell as the size of the messages. In particular, topological informationis utilized to minimize not just the number of messages, but also thenumber of hops between the devices 28-34 each message needs to make.

The proposed knowledge dissemination method propagates data from onedevice to another device in a distributed fashion. As a manual input inthe device settings, each device knows its immediate neighbor devices oneach side. An endpoint device is defined as a device that does not havean immediate neighboring device on one of its two sides or a device thatdefines the boundary of the division that the distribution automationsystem considers, such as open tie devices. For example, in the network10, the devices 28, 32 and 34 are all endpoint devices, where theboundaries of the division 48 are defined by open tie devices, which arethe normally open devices 32 and 34. The devices 28 and 30 are closed.

In the proposed dissemination method, the endpoint devices 28, 32 and 34will periodically initiate data dissemination into the division 48 astriggered by the timer 72, such as every five seconds. When the timer 72in each of the endpoint devices 28, 32 and 34 expires, the endpointdevices 28, 32 and 34 will reset their timer 72 to expire in the sameamount of time, and send a data dissemination message includinginformation and data it has stored about itself, such as voltages,currents, loads on sections, open/close status, etc., to their one-sideneighbor devices. For example, in the network 10, when the timer 72expires, the device 28 will reset its timer and send a datadissemination message to the device 30 containing its up-to-dateinformation, the device 32 will reset its timer and send a datadissemination message to the devices 30 and 34 containing its up-to-dateinformation, and the device 34 will reset its timer and send a datadissemination message to the devices 30 and 32 containing its up-to-dateinformation. Note that it is beneficial if the timers are GPSsynchronized, but it is not a requirement as discussed below. It is alsonoted that the communications of messages from one device to a nextdevice as described herein may reference a flow direction of themessages.

As soon as a non-endpoint device receives messages from all of itsneighbor devices on its message receiving side, it will send a messageto all of its neighbor devices on its message sending side along theflow direction, where the flow direction can be in either direction.This message will contain the information about the device itself, aswell as the information it has about every other device on its messagereceiving side. This includes the information from its immediateneighbor devices on the message receiving side and all of the devicesbeyond the immediate neighbor devices. For example, in the network 10,after the device 30 receives the message from the device 28, it willstore the information and send a data dissemination message to thedevices 32 and 34 containing the information about itself, as well asthe information about the device 28. Similarly, after the device 30receives the messages from the devices 32 and 34, it will store theinformation and send a data dissemination message to the device 28containing the information about itself, as well as the informationabout the devices 32 and 34. The non-endpoint devices know what devicesare on each of their sides in the division 48, and will not to send itsmessage until it receives the information from all of the devices on aparticular side. When a division boundary or endpoint device receivesmessages from all of its neighbor devices on one side, it will not senda message to all of its neighbor devices on the other side because theneighbor devices on the other side are in a different division. By thisprocess, at the end of each data dissemination period, each device willhave the information of all of the devices in the division 48.

FIG. 3 is a simplified schematic type diagram of an electrical powerdistribution network 80 illustrating an extreme linear case for the datadissemination process as discussed above. The network 80 includes an ACpower sources 84 and 86 and, in order from the source 84 to the source86, switching devices 90, 92, 94, 96 and 98, where the switching devices90 and 98 are endpoint devices and the switching device 98 is normallyopen. In this configuration, a division 82 is provided between thesource 84 and the device 98 and includes a feeder 88. When its timerexpires, the switching device 90 sends its information to the switchingdevice 92. When the switching device 92 receives the information fromthe switching device 90 it sends its information and the informationabout the switching device 90 to the switching device 94. When theswitching device 94 receives the information from the switching device92 it sends its information and the information about the switchingdevices 90 and 92 to the switching device 96. When the switching device96 receives the information from the switching device 94 it sends itsinformation and the information about the switching devices 90, 92 and94 to the switching device 98. Likewise, when its timer expires, theswitching device 98 sends its information to the switching device 96.When the switching device 96 receives the information from the switchingdevice 98 it sends its information and the information about theswitching device 98 to the switching device 94. When the switchingdevice 94 receives the information from the switching device 96 it sendsits information and the information about the switching devices 96 and98 to the switching device 92. When the switching device 92 receives theinformation from the switching device 94 it sends its information andthe information about the switching devices 94, 96 and 98 to theswitching device 90.

FIG. 4 is a simplified schematic type diagram of an electrical powerdistribution network 100 illustrating another extreme case for the datadissemination process as discussed above. The network 100 includes an ACpower source 102 and a division 104. The division 104 includes a feeder106 coupled to the power source 102, switching devices 108, 110, 112,114, 118, 122, 126, 130 and 132 coupled along the feeder 106, as shown,where the switching devices 108, 114, 118, 126, 128 and 130 are endpointdevices of the division 104. As above, along one flow direction, theswitching device 110 does not send its data dissemination message to theright until it receives the messages from the switching devices 108 and118, the switching device 122 does not send its data disseminationmessage until it receivers the messages from the switching devices 130and 132, the switching device 112 does not send its data disseminationmessage to the devices 110 and 112 until it receives the messages fromthe switching devices 110 and 122. Likewise, along another flowdirection, the switching device 112 does not send its data disseminationmessage to the left until it receives the messages from the switchingdevices 114 and 126, the switching device 122 does not send its datadissemination message to the switching devices 110 and 112 until itreceives the message from the switching devices 130 and 132, and theswitching device 110 does not send its data dissemination message to theleft until it receives the messages from the switching devices 112 and122 that include information from all of the switching devices 112, 114,122, 126, 130 and 132.

A self-tie is a series of two or more switching devices where everydevice is both different from and a neighbor device of the devicepreceding it, none of the devices in the series is an endpoint device,and the same devices are listed both at the beginning and the end of theseries. If there is a self-tie in the division, and no device in theself-tie is a division boundary device, then one device in the self-tiewill be designated as an endpoint device by a predefined rule asexplained below in paragraph [0046]. This prevents the datadissemination from entering an endless loop.

The discussion below is a comparison between the proposed datadissemination method and two other known data dissemination solutions,namely, a naïve solution and a centralized solution. In the naïvesolution, each switching device sends a message with its own informationto every other device. In the centralized solution, one of the devicesin a division is designated as a concatenator device. Each switchingdevice in the division will send a message to the concatenator devicewith its own information. After receiving messages from every device inthe division, the concatenator device will send a message with theinformation of the whole division to its neighbor devices, which willthen forward it to their neighbor devices and so forth. It is noted thatdue to geographical restrictions, when a switching device sends amessage to another device, the message may need to be routed throughmultiple devices. To simplify the comparison, it is assumed that eachdevice can only send direct messages to its immediate neighbor devices.Therefore, in order to send a message to another device that is not aneighbor device, the message will be routed through a neighbor deviceand the neighbor device's neighbor device until the destination usingthe shortest path according to the network topology. For example, in thenetwork 10, when the device 28 needs to send a message to the device 32,the device 28 will send the message to the device 30, and then thedevice 30 will send it to the device 32. To measure the message size, aunit of data is defined as the data containing the voltage and currentmeasures of one device.

Examples can be produced that show that the data dissemination methodproposed in this disclosure requires a relatively small number ofmessages compared to other methods, such as naïve and centralizedmethods, while the messages are still of a reasonable size. It is alsonoted that the average units of data each device sends (average numberof messages x average message size) is the minimum for the proposedapproach compared to other methods, such as naïve and centralizedmethods. This has a direct impact on the time it takes for each deviceto get the full picture of the division 48. These advantages of theproposed method are found in other types of network topologies as well,from linear structures, such as the network 80, to full tree structures,such as the network 100.

It is noted that for the centralized solution, the number of messagesdepends on the choice of the concatenator device. Finding a concatenatordevice that minimizes the number of messages in a complex network is nottrivial. Even if such a concatenator device can be found, it may notresult in fewer messages than the proposed method, and it may stillresult in more data being passed around than the proposed method. Themain disadvantage of the centralized solution is that if theconcatenator device of a division experiences any malfunction, no datawill be passed. Furthermore, if any communications link is down, thenthe devices downstream of the communications link in relation to theconcatenator device will not receive any data about their neighbordevices who are also downstream of this communications link.

For the proposed data dissemination method, it is beneficial to maintainthe information dissemination process relatively synchronized betweenthe devices. Specifically, the more synchronized the process is thenewer the information a device will have about other devices. For aswitching device that has multiple neighbor devices on the receivingside and at least one neighbor device on the sending side if it receivesmessages from all of the neighbor devices on the receiving side aroundthe same time, then it can immediately send a message to the neighbordevices on the sending side. By contrast, if it receives messages fromits receiving side neighbor devices one after another during a longertime span, then it has to wait for a longer time to send a message toits sending side neighbor devices, because it will only send the messageafter it receives the message from the last receiving side neighbordevice. This results in the information that a device has about thedistant devices to be relatively old.

If the devices have reliable synchronized clocks, it is straightforwardto synchronize the information dissemination between the devices. Inthis disclosure, an alternative method of roughly synchronizing theinformation dissemination through messaging for the cases where reliablesynchronized clocks are not available is also proposed. To do this, oneof the switching devices 28-34 in the division 48 is designated as thesynchronizer device, where the synchronizer device periodically sendsout sync messages to its neighbor devices. When a device receives a syncmessage from one side, it will propagate this message to all of theneighbor devices on the other side. When an endpoint device receives async message, it will reset its timer for data dissemination. If anendpoint device is selected as the synchronizer device, then it willreset its timer for data dissemination as soon as it initiates the syncmessages. The synchronizer device sends the sync messages at a muchlower frequency than the information dissemination messages. Forexample, the synchronizer device may initiate a sync message every fiveminutes, and the endpoint devices may initiate regular informationdissemination messages every five seconds. Note that this method doesnot require the synchronizer device to have a complete view of thedivision, where each device in the division only needs to know its ownneighbor devices on each side. Also note that this method can be used toinitiate data dissemination. Since the sync messages are propagated outfrom the synchronizer device, for different possible locations of thesynchronizer device in a division, the total number of sync messages forthe division 48 will be the same.

If the synchronizer device of a division experiences any malfunction,the information dissemination may not be synchronized. However, unlikethe concatenator device in the centralized dissemination method, in thiscase, the information dissemination will continue. The switching deviceswill still have updated information of all of the other devices, albeitwith longer delay. To regain synchronism after a division loses itssynchronizer device, a non-synchronizer device that does not receive async message for more than 1.5 times of the regular time interval forsync messages, will start sending out sync messages to its neighbordevices. While this may result in multiple devices thinking themselvesas the synchronizer device of the division, this can be resolved asexplained below.

In the case where more than one device thinks it is the synchronizerdevice of the division, they will all initiate sync messages. If adevice receives a sync message initiated from a different synchronizerdevice than the synchronizer device in its memory, it will determine ifthe new synchronizer device is more qualified as a synchronizer devicethan the old device based on predefined rules, such as the one with thehighest ID. If yes, it will update its own memory of the newsynchronizer device. If not, it will ignore this sync message and notpropagate it to other devices. Because this qualification processhappens in all devices including those who think themselves to be thesynchronizer device of the division 48 at the end of this process, onlythe most qualified device will remain the synchronizer device of thedivision 48.

To deal with possible self-ties that do not include a boundary device inthe division, as mentioned earlier in paragraph [0038], a device in theself-tie is designated as an endpoint device. This can be done byexploiting the sync messages. Specifically, if a device receives a syncmessage from one side and later receives a sync message from the otherside, both sync messages are initiated by the same synchronizer device,and the sync messages were originally sent from the same side of thatsynchronizer device, then this device is designated as a virtualendpoint device, and it does not propagate the second sync message. Thisis necessary because if the sync messages were originally sent from thedifferent sides of that synchronizer device, it means that thesynchronizer device itself is in the self-tie, and it is an endpointdevice itself, so there is no need to create a virtual endpoint device.

With distributed data dissemination methods as discussed herein, thedata messages are usually propagated from one device to another devicefollowing certain flow paths, where the goal is for each device to havethe full and current information of all of the other devices at the endof each dissemination process, and where a flow path can either be alinear path or a more complex graph structure with branching and joininglines. Any local interruption to the flow of messages, either momentaryor permanent, may block the regular flow of the data dissemination.Specifically, any momentary or intermittent interruption of thecommunications may prevent a device from obtaining updated informationabout another device for an extended period of time. And, if thecommunications problem is permanent, then a device may never get anyinformation about another device.

With any communications problem, some degradation in performance isinevitable. The purpose of the communications error handling is tominimize the impact of communications problems so that each device canstill have some information about the other devices. Although thisinformation may be incomplete and relatively outdated, it is better thannot having any information. In contrast, existing distributed datadissemination methods that rely on or assume perfect communications willcompletely stop data dissemination while communications problems exist,even if the problems are intermittent or restricted to only a fewdevices.

This disclosure proposes two communications error handling methods,where one method deals with short-term contingencies and the othermethod deals with long-term contingencies. When the communicationsproblem appears temporary, the logic for short-term contingencies willmaintain the flow of data dissemination despite the problem. When thecommunications problem appears permanent, the logic for long-termcontingencies will reroute the data dissemination to circumvent theproblem.

The following discussion illustrates the benefits of applying theproposed communications error handling methods and not applying them.For a one message loss error, the outcome without the proposed errorhandling is that all of the feeder data is two data disseminationperiods old and the outcome with the proposed error handling is that thefeeder data is still one data dissemination period old for adjacentsections and two data dissemination periods old for other sections,where when a fault occurs and the sections downstream of the fault needto be restored, information for sections farther away upstream of thefault is not needed. For intermittent message losses for severaldissemination periods, the outcome without error handling is the newestfeeder data would be the data collected before the first message loss,and the outcome with error handling is the feeder data is graduallyolder for devices farther away on the feeder. For permanentcommunications loss of a device, where devices on both sides of thatdevice experiencing communications loss can still communicate with eachother, the outcome without error handling is the newest feeder datawould be the data collected before the communications loss and faultrestoration performed on old loading data can lead to sub-optimalresults, and the outcome with error handling is the feeder data is up todate except for the loading distribution between the sections on the twosides of the problematic device and fault restoration will be optimal asthe device experiencing communications loss cannot be commanded tooperate anyway.

The network 80 shown in FIG. 3 can be used to describe the proposederror handling scheme when communications losses occur. As discussed,each endpoint switching device 90 and 98 periodically sends messages toits immediate neighbor switching devices 92 and 96. The non-endpointswitching device 92, 94 and 96 wait until they receive messages from allof their neighbor devices on one side, and then send the aggregatedinformation in a message to all of the neighbor devices on the otherside. For example, every t seconds, i.e., the data disseminationinterval, the device 90 sends a message containing its own data to thedevice 92. When the device 92 receives the message from the device 90,the device 92 will send a message to the device 94 with the data fromthe devices 90 and 92, and so on down the feeder 88. When the device 98receives a message from the device 96, the device 98 will just storeother devices' data from the message in its own memory. Similarly,another message will flow down the feeder 88 in the opposite directionfrom the device 98 to the device 90. After both message flows arefinished, all of the devices 90-98 will have the complete and updatedinformation of all of the other devices.

For the explanation of the proposed communications error handlingmethods, only the data dissemination flow from the device 90 to thedevice 98 will be described. In this explanation, the device 90 is theinitiator device because it initiates the data dissemination flow, thedevice 98 is the terminator device because the dissemination flow stopsat the device 98, and the other devices 92-96 are intermediate devices.For this flow, a from-neighbor device of a device is a neighbor devicethat this device receives messages from, and a to-neighbor device is aneighbor device that the device sends messages to. Note that thesedefinitions are specific to the particular message flow being discussed,and are only introduced for the discussion below. The devices 90-98themselves do not make these designations as each side of a device istreated exactly the same, and independently of the other side of thedevice. In other words, when a device disseminates aggregated deviceinformation to one side after receiving all of the messages from theother side, it does so regardless of how many messages it alreadyreceived from the other side. The only requirement for this scheme towork is that all of the endpoint devices send messages to their neighbordevices every data dissemination interval.

To handle short-term communications contingencies, the intermediatedevices 92-96 will use two timers. Whenever an intermediate device sendsa message to to-neighbor devices because it received message(s) fromfrom-neighbor devices, it will set its timer to expire in the timedefined as a backup interval, where it is required that a datadissemination interval is less than the backup interval, which is lessthan two times the data dissemination interval. The timer will be reseteach time the device sends a message. With this condition, whencommunications are working properly, the timers in the intermediatedevices 92-96 will always be reset before expiring. However, when amessage is lost during transmission, the timer in an intermediate devicemay expire. When the timer expires, this device will send a message tothe next device(s) along the flow direction even though it did notreceive a message from each of the preceding device(s) or from-neighbordevices. It will then set its timer to expire in the time of the datadissemination interval. For example, if the message sent from the device92 to the device 94 is lost, the timer in the device 94 will expire, andit will send a message to the device 96 although it did not receive amessage from the device 92. This message will contain the updatedinformation of the device 94, but the older information from the devices90 and 92. In this case, the device 94 is effectively a new initiatordevice for this round of data dissemination for this direction ofmessage flow. This results in the device 98 having the updatedinformation of the devices 94 and 96, but the older information of thedevices 90 and 92. Had the backup interval mechanism not beenimplemented, the device 98 would not have updated information of any ofthe other devices.

This short-term contingency handling logic is especially useful forintermittent down communications links. Assume that the communicationslink between the devices 92 and 94 and the communications link betweenthe devices 94 and 96 are not stable, where the messages sent from thedevice 92 to the device 94 and the messages sent from the device 94 tothe device 96 get lost about 50% of the time. In this particularexample, one of these two communications links is always down in anyround of the data dissemination flow. Then, as illustrated below inTables 9-13, after several rounds of data dissemination, the device 98will have relatively up-to-date information about the other devices90-96. The number in each box in the Tables 9-13 indicates how currentthe particular device stored data is relative to a certain round of datadissemination. For example, the memory in the device 98 holding theinformation of the device 90 with number 2 means the device 98 has theinformation of the device 90 from data dissemination round 2. Table 9 isthe stored data in each device 90-98 after data dissemination round 0,i.e., perfect communication, Table 10 is the stored data in each device90-98 after data dissemination round 1, i.e., the communications linkbetween the devices 92 and 94 is down, Table 11 is the stored data ineach device 90-98 after data dissemination round 2, i.e., thecommunications link between the devices 94 and 96 is down, Table 12 isthe stored data in each device 90-98 after data dissemination round 3,i.e., the communications link between the devices 92 and 94 is down, andTable 13 is the stored data in each device 90-98 after datadissemination round 4, i.e., the communications link between the devices94 and 96 is down. If the short-term contingency handling logic was notused in this example, then the device 98 would never have any updatedinformation about any of the other devices.

TABLE 9 90's 92's 94's 96's 98's memory memory memory memory memory 90's0 0 0 0 0 information 92's 0 0 0 0 information 94's 0 0 0 information96's 0 0 information 98's 0 information

TABLE 10 90's 92's 94's 96's 98's memory memory memory memory memory90's 1 1 0 0 0 information 92's 1 0 0 0 information 94's 1 1 1information 96's 1 1 information 98's 1 information

TABLE 11 90's 92's 94's 96's 98's memory memory memory memory memory90's 2 2 2 0 0 information 92's 2 2 0 0 information 94's 2 1 1information 96's 1 2 information 98's 2 information

TABLE 12 90's 92's 94's 96's 98's memory memory memory memory memory90's 3 3 2 2 2 information 92's 3 2 2 2 information 94's 3 3 3information 96's 3 3 information 98's 3 information

TABLE 13 90's 92's 94's 96's 98's memory memory memory memory memory90's 4 4 4 2 2 information 92's 4 4 2 2 information 94's 4 3 3information 96's 4 4 information 98's 4 information

For the long-term contingency handling, it is assumed that thecommunications layer in each switching device 90-98 can identify thestates of communications links between that device and the other devicesand store them in a communications connectivity table, i.e., whethereach device can receive messages from and transmit messages to the otherdevices. There are two flow directions and three possible states foreach communications link. For a certain device, its communications layeridentifies the other devices it can transmit messages to and the otherdevices it can receive messages from. The possible states for eachdirection of a communications link are Yes (√), No (x) and Unknown (?).The long-term contingency handling logic only takes effect when thecommunications layer decides that some of the communications links arenot in the Yes state. It is noted that if the device 90 can receivemessages from the device 92, then when the device 92 sends a message tothe device 90, the communications layer can find a route for themessage. This route could be one message directly from the device 92 tothe device 90, or multiple messages routed from the device 92 to thedevice 90 through other devices using an existing routing protocolprovided by the communications layer. As such, if the device 90 cannotreceive messages from the device 92, then there is no possible route forany message from the device 92 to the device 90.

The following are two examples of how such connectivity tables can beused. In the first example, the device 92 cannot send or receivemessages, where the corresponding connectivity Tables 14-16 of thedevice 90, the device 92 and the device 94, respectively, are shownbelow. From these tables, the device 90 and the device 94 cancommunicate with each other despite the device 92 being down. This maybe because the device 90 and the device 94 are within each other'stransmission range because there is a repeater between them or becausethere are other nearby devices on other feeders that can help route themessages between them.

TABLE 14 90 92 94 96 98 Transmit-to ? ✓ ✓ ✓ Receive-from x ✓ ✓ ✓

TABLE 15 92 90 94 96 98 Transmit-to ? ? ? ? Receive-from x x x x

TABLE 16 94 90 92 96 98 Transmit-to ✓ ? ✓ ✓ Receive-from ✓ x ✓ ✓

In the second example, assume that one direction of a communicationslink is down, for example, caused by vegetation, resulting in thedevices 90-98 breaking into two communications groups, where acommunications group is a subset of the devices such that any twodevices within this group can communicate with each other with two-waycommunications. In this example, the devices 90 and 92 in Group 1 canonly send messages to, but not receive messages from the devices 94-98in Group 2. The corresponding connectivity Tables 17-19 of the devices90-94, respectively, are shown below.

TABLE 17 90 92 94 96 98 Transmit-to ✓ ? ? ? Receive-from ✓ x x x

TABLE 18 92 90 94 96 98 Transmit-to ✓ ? ? ? Receive-from ✓ x x x

TABLE 19 94 90 92 96 98 Transmit-to x x ✓ ✓ Receive-from ✓ ✓ ✓ ✓

When the communications layer of a device detects that in itscommunications connectivity table, the entry for a from-neighbor devicedoes not have Yes for both directions, it will perform a graph search,such as a BFS or DFS, on the from-side of the device to find the closestdevices in the topology that have Yes for both directions, and assignthem as the new from-neighbor devices. It is assumed that when thenetwork is initially brought up online, or when devices are installed orremoved, there is some time interval in which all of the devicescommunicate with each other properly so they all have built anup-to-date topological view of their surroundings. For example, inconnectivity Table 16, when the communications are perfect, the oldfrom-neighbor device of the device 94 is the device 92. Since in theconnectivity Table 16 for the device 94, the device 92 no longer has Yesfor both directions, the device 94 will find the closest device on thefrom-side in its topology with Yes for both directions for its newfrom-neighbor device, where the new from-neighbor device is the device90.

In the connectivity Table 19 for the device 94, the device 92 is nolonger a from-neighbor device, and there is no qualified device as afrom-neighbor device for the device 94. Without a from-neighbor device,the device 94 becomes an initiator for the flow. Note that for thedevice 94, even though the device 92 is not a from-neighbor deviceanymore because the device 94 cannot transmit messages to the device 92,it is still possible that the device 94 can receive messages from thedevice 92. If a device receives a message from a known device that isnot a from-neighbor device, it will process and integrate the data inthe message, but will not trigger the sending of a message to itsto-neighbor devices.

Similarly, when the communications layer of a device detects that in itsconnectivity table, a to-neighbor device does not have Yes for bothdirections, it will perform a graph search on its to-side to find theclosest devices in the topology that have Yes for both directions, andassign them as the new to-neighbor devices. In addition, it will alsoadd the devices between itself and the new to-neighbor devices for up toL levels in topology as additional to-neighbor devices (L≥1), where Lcan be a user defined number such as 2. From those additionalto-neighbor devices, those who have a No for the transmit-to directionwill be excluded. For example, in the communications connectivity Table14 for the device 90, the device 94 becomes a new to-neighbor deviceand, for L=2, the device 92 is also a to-neighbor device since thedevice 90 is uncertain about whether the device 92 can receive messagesfrom it. In the connectivity Table 18 for the device 92, there is nodevice with two-way communications on the to-side and, for L=2, thedevices 94 and 96 will be added as the new to-neighbor devices, whichresults in the split of the flow for data dissemination. For Group 1,whenever the timer 72 for the left-right direction of message flow inthe device 90 expires, it sends a message to the device 92, and thedevice 92 sends messages to the devices 94 and 96. For Group 2, wheneverthe timer in the device 94 expires, it sends a message to the device 96,and the device 96 sends a message to the device 98. Note that thedevices 94 and 96 will receive messages from the device 92, but theywill only process and integrate the data in the messages. The flow ofthe data dissemination in Group 2 is still controlled by the timer inthe device 94. The end result is that the device 98 will have theinformation of all of the other devices 90-96. But, for another datadissemination flow from the device 98 to the device 90, theunidirectional down communications link makes it impossible for thedevice 90 to get updated information of the devices 94-98 in Group 2.

In distribution automation power networks of the type being discussedherein, it is important for the control devices to have updated loadinformation for each section in the network so as to know what loads canbe powered by what sources so that the sources are not overloaded whenload switching occurs in response to faults, where a section's boundaryis defined by switching devices or other current measuring devices. Theload of each section can either be computed by actual current andvoltage measurements of the switching devices on the boundary or byactual current and estimated voltage measurements of those devices.However, it is difficult to always get accurate and locally synchronizedmeasurements for the load computation. The purpose for computing updatedloading information is to enable automatic restoration from faults, orautomatic reconfiguring of the electric network for optimal loadbalancing. Specifically, to decide what extra network sections eachalternative source can power, the power being consumed in each sectionmust be known.

This disclosure also proposes a robust statistical method to computeload power that smooths out unstable measurements, which improves theexisting methods of computing loads in many aspects. In this disclosure,loads are considered at the section level. As referred to above, eachsection is defined as the powerlines bounded by the switching devices,or other devices capable of measuring current magnitude. This proposalworks the best for devices that are also capable of measuring voltages,but this is not required. In closed loop topologies where two or morepower sources are allowed to be combined to power the same loads, thedirection of the current flow with respect to voltage is assumed to bemeasurable by the use of phasor voltage and current measurements, remotesynchro-phasor voltage measurements combined with local synchro-phasorcurrent measurements, or other means. Using the method in thisdisclosure, if the measurements are in the phasor domain, i.e., complexvalues, the resulting power will be complex power. In radial topologies,if only current magnitude measurements are available, the method canstill be applied, although the results will only be power magnitudes.The control is assumed to have the network topology information becausethe load of each section is computed from the devices around thesection.

This loading estimation scheme must be accompanied by a communicationsscheme in which each device's latest voltage and current measurementsare periodically sent to the control, either directly or indirectlydepending on the data dissemination scheme. The control then computesthe updated load for each section. Alternatively, where there aremultiple controls distributed throughout the network, the computation ofthe load can be distributed such that a control at each section computesthe load for that section, and communicates the result to controls inother sections. Measurements of different devices may arrive at thecontrol at different times. At the end of each data disseminationperiod, the control should have received the latest measurements fromall of the devices. Such measurements can be the complex power flowingthrough each device. If the phasors, i.e., complex voltages andcurrents, are periodically sent to the control for other purposes, thenthere is no need to send complex powers in addition to the phasorsbecause the complex powers can be computed from the phasors.

The loads for the sections are computed from measured or derived powermeasurements, i.e., using the measured or estimated voltages andmeasured currents. The load of a section s for each phase p, where p canbe phase A, B or C, is the sum of the power flowing into the sectionfrom all of the devices around the section, i.e., net power flow, on thephase p. Assume that for a device k bounding a section s for phase p,the measured current is I_(k,p), the measured voltage, if available, isV_(k,p), and if the device lacks a voltage sensor, the estimated voltageis V_(e,k,p), where V_(k,p), V_(e,k,p) and I_(k,p) can be phasor valuesor just magnitudes depending on the measuring capability. Whereapplicable, ctp_(k,s) stands for the current transformer polarity, wherectp_(k,s)=1 if current flowing through the device k into section s ismeasured as positive current, and ctp_(k,s)=−1 otherwise. Table 20 belowshows how the power flowing through the device k into the section s onphase p, denoted as P_(k,s,p), is computed.

TABLE 20 Device's measure capability Power Calculation Measured voltagephasor V_(k, p) and current P_(k, s, p) = ctp_(k, s) × phasor I_(k, p)V_(k, p) × I*_(k, p) Estimated voltage synchrophasor V_(e, k, p)P_(k, s, p) = ctp_(k, s) × and current synchorophasor I_(k, p)V_(e, k, p) × I*_(k, p) Voltage magnitude V_(k, p) and currentP_(k, s, p) = ctp_(k, s) × magnitude I_(k, p) with some measure ofV_(k, p) × I_(k, p) × directionality, for example, by measuring thedir(I_(k, p)) time difference between the voltage's zero crossing andthe current's zero crossing; specifically, dir(I_(k, p)) = 1 if currentangle is close to voltage angle, or dir(I_(k, p)) = −1, if current angleis about 180° off of voltage angle Voltage magnitude V_(k, p) andcurrent P_(k, s, p) = V_(k, p) × I_(k, p) × magnitude I_(k, p), in aradial topology dir_(k, s) where dir_(k, s) = −1 if segment s is betweendevice k and the source, as determined by topology, and dir_(k, s) = 1otherwise Estimated voltage magnitude V_(e, k, p) P_(k, s, p) =V_(e, k, p) × I_(k, p) × and current magnitude I_(k, p) in a radialdir_(k, s) topology where dir_(k, s) is defined as above

If the device k is not equipped with a voltage sensor, the voltage atthe device k, as a phasor or just magnitude, must be estimated from themeasurement(s) of nearby device(s). For example, the voltage of thenearest voltage-measuring device can be used, or an average voltage canbe computed from several nearby voltage-measuring devices. In non-radialnetworks, if some switching devices are not equipped with a voltagesensor, all voltage and current measurements need to be phasors, andthese phasor measurements need to be synchronized (synchro-phasors). Inradial networks, nominal voltage can be used as well, where no actualvoltage sensing is required. If a step-down or step-up transformerexists between the device k and the voltage-measuring device, then thevoltage needs to be adjusted based on the transformer.

With the power of each switching device around the section s, the loadof this section on phase p is then L_(s,p)=ΣkeKs P_(k,s,p), where K_(s)is the set of all of the devices around this section. If phasors areused in the computation, then the load is a sum of complex values and isitself a complex value.

If there is load in a section having a constant-voltage source, i.e.,substation, and the control has no access to the measurements on thesource side of the section, then the load cannot be calculated with theabove described method. For example, in the section 38 of the network10, when computing the available additional power capacity the source 12can provide, which may be necessary to determine whether the source 12can provide power to additional sections for switching calculationsduring a fault event so that the source 12 is not overloaded, aconservative estimate can be used. More particularly, if the maximumpower that the source 12 can provide is P_(source), the maximum loadallowed on the section 38 is L_(max), and the load 24 on the section 38computed using the method above from measurements from the switchingdevice 28 is L₁, which should be negative since power is flowing out ofthe section 38, then the available additional capacity P_(addition) thatthe source 12 can provide is P_(addition)=P_(source)−L_(max)+L₁.

If there is a DG source, such as a solar, wind, turbine, battery, etc.,with constant power in a section, it will be treated as a negative load,where it would not be known how much power the source can provide or isproviding. In this case, the load calculation using the measurementsfrom other devices around this section will be the same as describedabove. For example, if the DG source 36 in the section 40 is outputtingmore power than the customers of the section 40 are consuming, i.e., theload 24, then the load of the section 40 will be negative using thecomputation described above. In other words, the load of the section 40that is computed using the computation described above is the sum of thepower output of the DG 36 and the power consumption of the load 24.

The control maintains a memory, for example, the memory 68, for eachdevice on each side to store the recent history of the measurements. Thememory 68 is used for the improvement of robustness and the handling ofunidentified transient behaviors due to faults, switching, etc. The sizeof the memory 68 for each side of each device is fixed. Whenever a newmeasurement is received, it will be stored in the corresponding memory,and the oldest value of that measurement in the memory 68 is erased.

To handle transient behaviors due to faults, switching, etc. and smoothout unstable measurements, instead of computing the section load fromthe latest measurements, the median filter 74 using N recentmeasurements is applied for the load computation. Specifically, for thedevices around a section, with the recent history of the measurements inthe memory 68, Load #1 is computed from the latest measurements of eachdevice, Load #2 is computed from the second latest measurements of eachdevice, . . . , and Load #N is computed from the Nth latest measurementsof each device. Then, the median of Load #1, Load #2, . . . , Load #N istaken, and this median value is used as the load for that section.

The reason that a median filter is chosen over other possible filters isthat a median filter can handle up to (N−1)/2 outliers with N samples.In other words, if up to (N−1)/2 samples are affected by arbitrarilylarge errors, the median estimate will still be based on one of thecorrect remaining samples. In contrast, by that definition, an averagefilter cannot properly handle even a single outlier. Another feature ofa median filter is that for most of them, the filtered result matchesone of the sampled values.

There are different types of median filters suitable for loadingcomputations with two-dimensional sample points. This is the case whenthe power is represented as a complex value, one dimension being thereal part (active power) and the other dimension being the imaginarypart (reactive power). One example is described below of such a medianfilter for complex power. For N complex numbers c₁, c₂, . . . , c_(N),the median of the real part M_(Re)=median_(n=1, . . . ,N){Real(c_(n))}and the median of the imaginary partM_(im)=median_(n=1, . . . ,N){Imaginary(c_(n))} are computed. Theseparts are then combined as the reference point M_(Ref)=M_(Re)+iM_(im).Note that M_(Ref) may not belong to the set of the sample points.Finally, a complex number is chosen in the samples that is the closestto the reference point M_(Ref) as the median of the samples, i. e.,M=argmin_(cn=c1,c2, . . . ,cN){|c_(n)−M_(Ref)|} Another possiblealternative median filter to the above one is the geometric median. Ingeneral, geometric medians are computationally more intensive.

The following is an example illustrating the issues with computing loadsin sections using only the latest measurements, but not using themeasurement stored in the memory 68 and the median filter 74. FIG. 5 isa simplified illustration of an electrical power distribution network140 including an AC source 142, a feeder 144 coupled thereto, andswitching devices 146, 148 and 150 coupled to the feeder 144, where asource section 152 is defined between the source 142 and the device 146,a load section 154 is defined between the devices 146 and 148, a loadsection 156 is defined between the devices 148 and 150 and a loadsection 158 is defined downstream of the device 150, and where thesection 154 has a load of 160, the section 156 has a load of 162 and thesection 158 has a load of 164, where the load 160 is 50 kW, the load 162is 20 Kw and the load 164 is 40 kW.

At a first step, the device 146 takes load measurements, calculates thepower flowing through the device 146, which is 110 kW in this examplebecause of the total load downstream of the device 146, and sends thepower calculation to the device 148. At a second step, the device 148takes current and voltage measurements, calculates the power flowingthrough the device 148, which is 60 kW in this example because of thetotal load downstream of the device 146, and sends the powercalculations for both of the devices 146 and 148 to the device 150. At athird step, the device 150 takes current and voltage measurements andcalculates the power flowing through the device 150, which is 40 kW inthis example. With the data collected by the device 150, the load ineach of the sections 154, 156 and 158 can be calculated correctly at 50kW, 20 kW and 40 kW.

If the device 148 receives the power of 110 kW flowing through thedevice 146, but before the device 148 can take a voltage and currentmeasurement, a fault may occur in the section 158, which increases thepower consumption in the section 158 by 50 kW. If this happens, in thesecond step when the device 148 takes the current and voltagemeasurements, it will include the extra consumption and its calculationof power flowing through itself, i.e., the device 148 will be 110 kW. Inthe third step when the device 150 takes the load measurements and triesto calculate the load in each of the sections 154, 156 and 158, the loadfor the section 154 will be incorrectly calculated as 0 kW because thedevice 150 thinks he power flowing through the device 146 is 110 kW, andthe power flowing through the device 148 is also 110 kW. Thismiscalculation is caused by the fault. Using the measurement memory 68and the median filter 74 as discussed in this disclosure, the outliercaused by the measurement mismatch in this example will be filtered out,and the resulting section loading will be the loading during normalconditions. That is what is desired for applications such as automaticfault restoration.

An alternative approach to solve the issue in this example is to rejectany measurement that is associated with a fault. This requiresadditional rules and filtering criteria for identifying a fault, and itwould be difficult to capture all of the possible fault scenarios. Bycontrast, the proposed approach using the measurement memory 68 and themedian filter 74 does not need to specify such rules and criteria, andcan reject other transient behaviors that may not be associated withfaults.

In certain cases, such as when any one of the devices 146, 148 and 150reports a loss of voltage, i.e., the voltage is below a predefinedthreshold, the measurements in the memory 68 should not be used forloading computations because the loads computed from such measurementsmay be incorrect. For this reason, this disclosure proposes that duringa data dissemination period, if any device 146-150 reports loss ofvoltage, the latest measurements of the devices that have been sent tothe control are discarded in the memory. When the control receives themeasurements from the remaining devices during the same datadissemination period, those measurements are not accepted. After theretraction, since the memory 68 has the size of N+1, the median filter74 for load computation still has enough measurements to compute theload using the median of the recent N measurements without disturbingevents.

In the example discussed above, assume that after the second step, thefeeder 144 loses power from the source 142. If memory retraction is notused, then after receiving (N+1)/2 measurements since the loss ofvoltage, the loads on all of the sections 154, 156 and 158 will becomputed as zero. These are not the loads desired for the computation ofautomatic restoration. Using the mechanism in this proposal, when thesource 142 is lost, at least one of the devices 146-150 will report aloss of voltage. Therefore, the latest measurements of this new periodof data dissemination are discarded. Assuming the remaining recentmeasurements in the measurement memory are the same as referred toabove, the load calculation will still be correct and reflect the loadper section prior to the loss of voltage, which is desired. Thesedesired loading values will stay the same even if the loss of voltagelasts for an extended time. This is because for every new disseminationperiod, the new measurements will not be recorded by the memory 68 dueto the loss of voltage.

During changes in topology when the current may be coming from adifferent source, combining power flow measurements taken before andafter the topology change will lead to erroneous load calculatingresults. In addition, topological changes, which typically follow adisturbance, may lead to a change in loading, for example, because a DGdropped offline. Therefore, when the control makes a change, or is awareof changes in topology that may directly change the section loads, it isfaster to obtain the changed loads if the loading computation only usesthe measurements after the change. When such control-aware changesoccur, the control will clear the memory 68 by discarding the existingmeasurements and saving the updated measurement in the memory 68. Atthis point, the memory 68 will contain only one recent measurement. Notethat before the memory 68 is filled with at least N measurements, themedian filter 74 used for computing the loading can be applied to thefewer measurements in the memory 68. With the continuation of receivingupdated measurements, the memory 68 will eventually be filled with N+1recent measurements again.

If the memory 68 is not cleared after the control-aware changes, usingthe median filter 74, the new values would only be reflected afterreceiving more than (N+1)/2 updated measurements. That would take thetime of (N+1)/2 periods of data dissemination. Moreover, if the changecaused a significant increase in the section loads, the slow updatewould put the network at risk of overloading the power sources. Oneexample is a DG, which is modeled as negative load. When a DG goesoffline due to reasons such as fault protection of the main feeder, thecontrol immediately knows this. The control then should assume that thesection with the DG has a load of zero. If merely the measurement givingzero load was added to the memory 68, but the older measurements in thememory 68 were not cleared, then using the median filter 74, a faultrestoration logic would think this section is still outputting powerbecause of the negative load, and try to restore extra loads that shouldnot be restored.

If at the end of a data dissemination period the control has notreceived the latest measurements from some devices, the loadingcomputation using the median filter 74 proceeds unchanged. Immediatelyfollowing the data loss, this may result in the load being computed frommeasurements taken at different data dissemination periods. However,assuming the load changes slowly relative to the data disseminationinterval, this should result in negligible error in the loadcomputation. Furthermore, after a few data dissemination periods with nocommunication contingency, the measurements in the memories 68 willrealign automatically so that again loading will only be computed frommeasurements taken at the same data dissemination period.

If a certain device lost communications, the control in other devices orthe control center 50 will not receive any updated measurements fromthat device. The loss of communications of that device should bedetected by the control's communications layer or other methods such asa timer in the control. As soon as the control detects the loss ofcommunications of the device, it computes and stores the ratio of theload magnitudes of the section on two sides of the device using the lastupdated loads of these sections. Later, when the control receives theupdated measurements from devices other than the non-communicatingdevice, it computes the combined load of the sections on two sides ofthe non-communicating device, and then it distributes the combined loadsto the sections using the saved ratios from the last actual loads.

For example, in the network 10, if the device 30 lost communications,and the last computed loads of the section 40 and the section 42 are 40kW and 20 kW, respectively, then the control stores the ratio of theloads between the section 40 and the section 42, which is 2:1. Then,with the topology information known to the control, it uses themeasurements of the devices 28, 32 and 34 to compute the combined loadof the section 40 and the section 42. If the combined load is 66 kW,then it records 44 kW for the load of the section 40 and 22 kW for theload of the section 42.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

What is claimed is:
 1. A method for calculating loads throughout a powerdistribution network, the network including at least one power source, aprimary feeder, a plurality of switching devices positioned along theprimary feeder and a section between switching devices, wherein the loadon a section is the sum of the power flowing into the section from allof the switching devices around the section, and wherein the pluralityof switching devices are in communication with each other, the methodcomprising: determining a first downstream load by a first switchingdevice provided on the feeder downstream from the power source usingcurrent and/or voltage measurements; sending a total downstream load toa second switching device provided on the feeder downstream from thefirst switching device; determining a second downstream load by thesecond switching device using current and/or voltage measurements;sending a total downstream load to a next switching device provided onthe feeder downstream of the second switching device; continuingdetermining and sending downstream loads to the switching devicesprovided along the feeder downstream of the next switching device inthis manner to a last switching device on the feeder; and calculatingthe load in each section along the feeder using the determined loads. 2.The method according to claim 1 further comprising knowing that a faulthas occurred in the network if calculating the load in each sectiongives an incorrect load calculation in one of the sections.
 3. Themethod according to claim 1 wherein each switching device includes amemory for an upstream side and a memory for a downstream side of thedevice, the memories storing a plurality of the determined loads takenat previous sample times.
 4. The method according to claim 3 wherein anoldest determined load is discarded when a new load is received.
 5. Themethod according to claim 3 wherein each switching device includes amedian filter, and wherein determining the loads includes determiningthe loads in a division as a median of a recent determined load and pastdetermined loads.
 6. The method according to claim 5 wherein the medianfilters use two-dimensional sample points for determining the loads foractive and reactive power.
 7. The method according to claim 3 furthercomprising suspending determination of the load in a switching device ifany of the switching devices reports a loss of voltage.
 8. The methodaccording to claim 7 wherein determining a load includes usingpreviously stored measurements before the loss of voltage.
 9. The methodaccording to claim 7 wherein determining a load includes usingpreviously stored measurements if a short-term data dissemination lossoccurs in the network.
 10. The method according to claim 3 whereindetermining a load includes computing and storing a ratio of loadmagnitudes of the sections using previously stored loads if a long-termdata dissemination loss occurs in the network.
 11. The method accordingto claim 3 further comprising clearing the memories if a known change ina topology of the network occurs.
 12. The method according to claim 1wherein calculating the load in each section along the feeder using thedetermined loads occurs in a control device.
 13. The method according toclaim 12 wherein the control device is one of the switching devices,more than one of the switching devices or a sub-station.
 14. The methodaccording to claim 1 wherein the current and/or voltage measurements arephasor values or magnitudes depending on the measuring capability. 15.The method according to claim 1 wherein the switching devices arereclosers, sectionalizers or circuit breakers.
 16. A method fordetermining loads throughout a power distribution network, the networkincluding at least one power source, a primary feeder, a plurality ofswitching devices positioned along the primary feeder and a sectionbetween switching devices, wherein the plurality of switching devicesare in communication with each other, the method comprising: measuringcurrent and/or voltage on one or both of an upstream side and adownstream side of each of the switching devices; calculating a load ineach of the switching devices using current and/or voltage measurementsat predetermined sample times; storing a plurality of the calculatedloads for consecutive sample times; determining a median load from apredetermined number of the loads stored; sending the median load fromthe switching devices to a control device; and calculating a load ineach of the sections in the control device.
 17. The method according toclaim 16 further comprising knowing that a fault has occurred in thenetwork if calculating the load in each section gives an incorrect loadcalculation in one of the sections.
 18. The method according to claim 16wherein the control device is one of the switching devices, more thanone of the switching devices or a sub-station.
 19. A system fordetermining loads throughout a power distribution network, the networkincluding at least one power source, a primary feeder, a plurality ofswitching devices positioned along the primary feeder and a sectionbetween switching devices, wherein the plurality of switching devicesare in communication with each other, the system comprising: means formeasuring current and/or voltage on one or both of an upstream side anda downstream side of each of the switching devices; means forcalculating a load in each of the switching devices using current and/orvoltage measurements at predetermined sample times; means for storing aplurality of the calculated loads for consecutive sample times; meansfor determining a median load using from a predetermined number of theloads stored; means for sending the median load from the switchingdevices to a control device; and means for calculating a load in each ofthe sections in the control device.
 20. The system according to claim 19wherein the control device is one of the switching devices, more thanone of the switching devices or a sub-station.